Field of the Invention
The formation of sulfonate-containing polymers has been clearly defined in a number of U.S. Pat. Nos.: 3,642,728; 3,836,511; 3,847,854; 3,870,841; and 3,877,530. These patents teach the formation of sulfonate polymers by contacting a polymer having olefinic unsaturation with a sulfonating agent.
This application differs from the previously identified U.S. patents in that the instant process is directed at the free radical solution polymerization of two polymerizable sulfonate-containing monomers such as sodium-N-(4-sulfophenyl)-maleimide monomer and a sulfonated styrenic monomer to form an alternating water soluble copolymer having a 50 mol. % portion of the sodium-N-(4-sulfophenyl)-maleimide monomer units and a 50 mol. % portion of the sulfonated styrenic monomer units. The sulfonated styrenic monomer is characterized by the formula: ##STR2## wherein Y.sup.+ is a cation selected from the Groups IA, IIA, IB or IIB of the Periodic Table or an amine of the formula .sup.+ NHR.sub.1 R.sub.2 R.sub.3 where R.sub.1, R.sub.2 and R.sub.3 can be aliphatic groups of C.sub.1 to C.sub.12.
The formed water soluble copolymers contain about 50 mol. %, due to the alternating nature of the copolymerization of sodium-N-(4-sulfophenyl)-maleimide. The sulfonated styrenic comonomer is also contained in about 50 mol. %.